The present invention relates to highly breathable and biodegradable films that demonstrate enhanced ductility. More particularly, the present invention relates to methods of making highly breathable films and precursor films comprising a biodegradable polymer and a polymer that is water soluble or water degradable.
Disposable absorbent products currently find widespread use in many applications. For example, in the infant and child care areas, diapers and training pants have generally replaced reusable cloth absorbent articles. Other typical disposable absorbent products include feminine care products such as sanitary napkins or tampons, adult incontinence products, and health care products such as surgical drapes or wound dressings. A typical disposable absorbent product generally includes a composite structure including a topsheet, a backsheet, and an absorbent structure between the topsheet and backsheet. These products usually include some type of fastening system for fitting the product onto the wearer.
Disposable absorbent products are typically subjected to one or more liquid insults, such as of water, urine, menses, or blood, during use. As such, the outer cover backsheet materials of the disposable absorbent products are typically made of liquid-insoluble and liquid impermeable materials, such as polypropylene films, that exhibit a sufficient strength and handling capability so that the disposable absorbent product retains its integrity during use by a wearer and does not allow leakage of the liquid insulting the product.
Although current disposable baby diapers and other disposable absorbent products have been generally accepted by the public, these products still have need of improvement in specific areas. For example, many disposable absorbent products can be difficult to dispose of. For example, attempts to flush many disposable absorbent products down a toilet into a sewage system typically lead to blockage of the toilet or pipes connecting the toilet to the sewage system. In particular, the outer cover materials typically used in the disposable absorbent products generally do not disintegrate or disperse when flushed down a toilet so that the disposable absorbent product cannot be disposed of in this way. If the outer cover materials are made very thin in order to reduce the overall bulk of the disposable absorbent product so as to reduce the likelihood of blockage of a toilet or a sewage pipe, then the outer cover material typically will not exhibit sufficient strength to prevent tearing or ripping as the outer cover material is subjected to the stresses of normal use by a wearer.
Furthermore, solid waste disposal is becoming an ever increasing concern throughout the world. As landfills continue to fill up, there has been an increased demand for material source reduction in disposable products, the incorporation of more recyclable and/or degradable components in disposable products, and the design of products that can be disposed of by means other than by incorporation into solid waste disposal facilities such as landfills.
As such, there is a need for new materials that may be used in disposable absorbent products that generally retain their integrity and strength during use, but after such use, the materials may be more efficiently disposed of. For example, the disposable absorbent product may be easily and efficiently disposed of by composting. Alternatively, the disposable absorbent product may be easily and efficiently disposed of to a liquid sewage system wherein the disposable absorbent product is capable of being degraded.
Many of the commercially-available biodegradable polymers are aliphatic polyester materials. Although fibers prepared from aliphatic polyesters are known, problems have been encountered with their use. In particular, aliphatic polyester polymers are known to have a relatively slow crystallization rate as compared to, for example, polyolefin polymers, thereby often resulting in poor processability of the aliphatic polyester polymers. Most aliphatic polyester polymers also have much lower crystallization temperatures than polyolefins and are difficult to cool sufficiently following thermal processing. In addition, the use of processing additives may retard the biodegradation rate of the original material or the processing additives themselves may not be biodegradable.
Also, while degradable monocomponent fibers are known, problems have been encountered with their use. In particular, known degradable fibers typically do not have good thermal dimensional stability such that the fibers usually undergo severe heat-shrinkage due to the polymer chain relaxation during downstream heat treatment processes such as thermal bonding or lamination.
For example, although fibers prepared from poly(lactic acid) polymer are known, problems have been encountered with their use. In particular, poly(lactic acid) polymers are known to have a relatively slow crystallization rate as compared to, for example, polyolefin polymers, thereby often resulting in poor processability of the aliphatic polyester polymers. In addition, the poly(lactic acid) polymers generally do not have good thermal dimensional-stability. The poly(lactic acid) polymers usually undergo severe heat-shrinkage due to the relaxation of the polymer chain during downstream heat treatment processes, such as thermal bonding and lamination, unless an extra step such as heat setting is taken. However, such a heat setting step generally limits the use of the fiber during in situ nonwoven forming processes, such as spunbond and meltblown, where heat setting is very difficult to be accomplished.
Additionally, one of the more important components of many personal care articles is the body-side liner. The liner is usually made of a surfactant-treated polyolefin spunbond. For a spunbond to be implemented as a liner, it is desired that the material be wettable to promote intake of fluid insults. In addition to rapid intake, it is desired that the composite absorbent product keep the user""s skin dry. In addition, it is desirable for the spunbond material to feel soft against the skin. The current spunbond diaper liner has a number of problems associated with it. First, it includes polyolefinic materials and does not degrade. Due to the hydrophobic nature of these materials, the liner must be treated with a surfactant to make it wettable. Because there is no permanent anchoring of the surfactant to the polyolefin, it has a tendency to wash off during multiple insults, increasing intake times of the nonwovens.
Furthermore, articles having a layer of a degradable polymer are relatively inflexible and do not offer a significant degree of breathability, making some articles uncomfortable to use for an extended period of time.
Accordingly, there is a need for an article that is biodegradable with enhanced ductility and breathability.
The present invention solves the above described problem by providing a method of producing highly breathable and biodegradable films that demonstrate enhanced ductility. The method includes blending a water soluble polymer and a biodegradable polymer to form a blended polymer mixture. The blended polymer mixture is then formed into a precursor film, using standard processes such as casting and blowing. The precursor film is further processed to form a biodegradable film, wherein the biodegradable film has a water vapor transmission rate of greater than about 2500 g/m2/24 hrs.
More particularly, the method includes stretching the precursor film to form the biodegradable film. The precursor film may be contacted with a solvent during the stretching process. In addition, the method may include etching the water soluble resin, and/or freeze-drying the precursor film. The precursor film may be freeze-dried by immersing the film in a solvent to swell the film followed by immersing the film in liquid nitrogen. The precursor film is then returned to room temperature under vacuum.
Still more particularly, the biodegradable film has an elongation at break of greater than about 100%, and the precursor film has an elongation at break of greater than about 350%. Further, the biodegradable polymer is preferably a biodegradable aliphatic polyester, and the water soluble polymer is preferably polyethylene oxide and/or polyethylene glycol. In addition, the biodegradable polymer is desirably in the form of a biodegradable polymer resin, and the water soluble polymer is in the form of a water soluble polymer resin.
Other objects, features and advantages of this invention will become apparent upon reading the following detailed description in conjunction with the figures and claims.